This application claims the benefit of Italian Application No. SV99A000036 filed Nov. 5, 1999 and PCT/EP00/10795 filed Nov. 2, 2000.
The invention relates to a damping corrugator roll, comprising an outer toothed surface, whose teeth extend over a certain axial length of the roll, support means allowing rotation about the axis of the roll, and rotary drive means.
The invention particularly relates to a corrugator roll of the above type, provided in combination with an upper corrugator roll, parallel and tangent to said lower roll, both rolls being part of a corrugator unit for paper sheets, in corrugated board fabrication.
As a rule, the upper corrugator roll has a greater diameter and is rotatably driven, but it also has peripheral skirt teeth, whereby it meshes with the teeth of the lower corrugator roll, which runs idle and is rotatably dragged along by the upper corrugator roll.
In prior art machines, a severe problem is the very high level of noise generated by the corrugator unit. This noise is caused by the generation of vibrations and oscillations, mainly in the lower corrugator roll, which, according to current manufacturing trends, is smaller than the upper corrugator roll, hence more exposed to the excitation of vibrations.
There may be different kinds of vibrations, i.e. they may depend on flexures transverse to the axis of rotation, or on torsional flexures, i.e. in the circumferential direction with respect to the axis of the roll. Vibrations also depend of the shape of the corrugator teeth of the two rolls which, in combination with the paper feed, cause the vibratory motion of the roll. Due to the considerable axial lengths of rolls, the vibratory and/or oscillatory effects are particularly felt in the center part of the roll, i.e. far from the support constraints at the ends thereof. Also, in this center part, the vibratory and/or oscillatory effects are relatively out of control and dependent on the features of the processed paper.
Prior art damping means can absorb or damp at least part of the vibrations at the end constraints of the lower corrugator roll, but definitely cannot handle neither systematic nor casual oscillations or vibrations (the latter due to modified features of the paper being processed) at the center part of the corrugator roll. Therefore, a relatively poor damping effect is always obtained, whereby to date a still high level of noise is generated by corrugator units, such that it requires expensive and complex acoustical treatments on machines.
Moreover, vibrations and/or oscillations cause functional problems, such as the need to limit the production rate because the poor vibration dampening causes a loss of attachment between the layers of the corrugated board and a smaller flute width.
The invention has the object to provide a damped, particularly lower corrugator roll, so that, by simple and relatively inexpensive arrangements, the drawbacks of prior art rolls can be obviated, by effectively damping the generation of vibrations and/or oscillations, hence by drastically reducing the noise effect and the functional drawbacks due to poor damping.
The invention achieves the above objects by providing a corrugator roll as described hereinbefore, comprising:
A cylindrical core which is supported for free rotation at its ends and whereon a toothed peripheral cylindrical jacket is supported in a floatable manner by an interposed or bearing material.
The bearing or interposed material may consist of a fluid, such as a gas, a liquid, a highly viscous liquid or, for instance, having a pasty consistency, or of a solid material having a highly hysteretic elastic behavior.
The characteristics of the gaseous, liquid or pasty fluid shall be such that the friction coefficient of said materials with respect to the surfaces in contact therewith, that is the outer skirt of the core and the inner skirt of the floating jacket, will increase as the relative speed between the floating jacket and the cylindrical core increases.
The interposed or bearing fluids may be provided under pressure, at atmospheric pressure, or in conditions of negative pressure with respect to external atmospheric pressure. This depends on the conditions of use.
It may be also provided that the jacket and the cylindrical core form, e.g. by using rotary sealing heads, a sealed hollow space wherein the interposed material is introduced and replaced from time to time after a predetermined number of operating hours.
Alternatively, the sealed hollow space formed by the tubular cylindrical jacket and by the cylindrical core may have inlets and outlets for automatic feeding of or filling up with the interposed material, in this case fluid, or for generating a continuous or batch circulation of said fluid, which can provide balanced dynamic conditions in the hollow space as regards pressure and quantity of fluid. At the same time, the circulation of fluid ensures a constant renewal thereof, for instance with respect to the maintenance of a predetermined temperature or of a predetermined mixture composition or condition, or of any other parameter that can be affected by the use and restored by service treatments.
Advantageously, the sealing means at the heads of the tubular toothed cylindrical jacket are such that they allow, by using yielding members, the jacket to be moved at least transverse to the core.
The cylindrical jacket has lower weight and inertia values as compared with the central core.
Depending on the length, the length to diameter ratio of the lower roll, i.e. of the jacket of the lower roll is higher than 10. The jacket shall be relatively thin, but anyway have a sufficient thickness to allow paper processing.
As a rule, the diameter to thickness ratio is of 8/1 to 15/1, preferably of about 10/1.
For diameters and lengths commonly used in corrugator machines, the thickness of the jacket may range from 10 to 100 mm, particularly from 20 to 50 mm, preferably from 25 to 35 mm.
The hollow space or chamber, or the difference between the outside diameter of the core and the inside diameter of the jacket is of 0,1 to 5 mm, also depending on the diameter and length of the jacket as well as on the type of interposed material.
The outer jacket can be made of any suitable material, also composite or in two, three or more layers.
For instance, the material to be used can be steel or other metals, preferably after undergoing hardening treatments, such as quenching or coating with hard layers, e.g. made of tungsten carbide, hard chromium or titanium nitrides.
The invention is based on the acknowledgement that, during operation, the vibrations in the floating jacket cause variations in the bearing thickness (thickness of the hollow space between the floating jacket and the cylindrical core), hence in the bearing fluid. Bearing thickness deformations cause variations in the relative speed of the filling or bearing material, hence variations in the friction coefficient, which have the effect of damping the motions and stresses that generate vibratory motions.
The arrangement according to the invention leads to unexpected advantages in combination with bthe toothed corrugator rolls. An effectively damping lower corrugator roll is the most appetizing and required thing in the field. A drastic reduction of the noise generated by vibrations would allow to reduce economic and construction efforts for acoustical treatments. Yet, the floating suspension of the lower corrugator roll does not require to account for the specificity of shapes or profiles of the corrugator teeth, since such floating suspension allows a wide adaptability to the teeth shapes, as regards both noise generation and functional effectiveness of the corrugator unit. More particularly it has to be noted that the teeth of corrugator rolls cooperating with each other are not designed to lead to a homocinetic kind of motion. This means that the way two corrugator rolls cooperate with each other is not similar to the way as two gears cooperate with each other, since the teeth are designed in order to corrugate sheets of paper without damaging the paper. The corrugator rolls are affected not only by vibration modes due their own motion but also by vibrations which are induced by the teeth and the paper being treated. The bearing fluid or material interposed between the core of the roll and the toothed jacket has shown a high speed of reacting to the induced vibrations thus leading to an effective damping of the vibrations which was unexpected in the technical field on the light of the actual knowledge.
Further unexpected advantages consist in the fact that the bering fluid or material leads to a uniform distribution of the pressure exerted by the corrugator roll over its entire length. This effect allows to avoid particular shaping of the corrugator roll with respect to a cylindrical form. Furthermore, the supports at the ends of the corrugator roll are less stressed than in then case of the known corrugator rolls. Thanks to the above advantages also the frequency of regeneration of the corrugator rolls is reduced, lowering costs for the manufacturers and obviating to have a production line stopped for longer time. It has to be noted that corrugator rolls are very large and big so that it is not quite simple to send the rolls back to the manufacturer for regeneration. Also the regeneration treatment is expensive and time consuming.
A particular advantage appears applying the contruction of the corrugator roll according to the present invention in combination with a corrugator unit, particularly for sheets or webs of paper, or similar, of the type comprising at least two rolls having a toothed or corrugated surface and being mutually engaged and pushed against each other by a predetermined pressure or force, the mutual compression between rolls being exerted over the whole axial length of the rolls through mechanical or magnetic means as described in EP 98112227.8.
In this case a cradle made of a series of several wheels or belts. Particular advantages results in a corrugator unit of the above mentioned kind in which one of the at least two corrugator rolls has a smaller diameter than the other roll.
The damping effectiveness obtained by the roll according to the invention also allows to improve the functionality of the corrugator unit, e.g. with reference to the possibility of increasing the corrugated board production rate, without incurring in manufacturing defects, such as gluing defects and/or variations in flute width.
The invention also relates to further improvements, which form the subject of the dependent claims.
The characteristics of the invention and the advantages derived therefrom will appear more clearly from the following description of a non-limiting embodiment, illustrated in the annexed drawings, in which:
FIGS. 1 and 2 are a schematic axial sectional view and a schematic transverse sectional view respectively of a roll according to the invention.
FIG. 3 is an axial sectional view of an embodiment of a roll according to the invention.
FIG. 4 is an axial sectional view of the outer toothed cylindrical jacket.
FIG. 5 is an axial sectional view of the sealing heads of the cylindrical jacket.
FIG. 6 is a view of the cylindrical core.
FIG. 7 shows a general corrugator unit with a pair of toothed rolls, an upper and a lower roll.